In recent years, fraud and malicious solicitation, using a telephone line are becoming social problems. To address these problems, techniques of detecting a call related to such a fraud by recognizing a voice during a call via a telephone line have been proposed (refer to, for example, Japanese Laid-open Patent Publication Nos. 2007-96962, 2008-210085, and 2006-196949).
For example, a telephone device disclosed in Japanese Laid-open Patent Publication No. 2007-96962 converts voice of a caller into a character string, compares keywords with the character string, and counts the number of matches for each keyword. When a plurality of keywords match the character strings, the telephone device determines that the call is made by a swindler.
A billing fraud preventing system disclosed in Japanese Laid-open Patent Publication No. 2008-210085 checks voice characteristics on the basis of voice data received from a user telephone terminal and voice data of preliminarily registered swindlers. The system converts the call voice data to a text and checks to see whether account information included in the text-converted call content matches with account information for fraud which is preliminarily registered. Further, the system calculates match rate between pre-registered keywords and keywords included in the text-converted call content. The system determines the determination level on the basis of the voice characteristics, account information, and match rate.
Further, in a telephone with a call content warning disclosed in Japanese Laid-open Patent Publication No. 2006-196949, when a pre-registered word is detected from content of a call recorded, information of the detection result is notified as a warning to the outside.
In those techniques, voice recognizing process is continuously executed on voice of at least one of speakers during a call. Consequently, process load caused by executing the voice recognition is heavy. On the other hand, a technique for reducing the process load of the voice recognizing device has been proposed (refer to, for example, Japanese Laid-open Patent Publication No. H10-155163). A telephone disclosed in Japanese Laid-open Patent Publication No. H10-155163 detects whether a transmitter-side voice signal is a sound signal or not, detects whether a receiver-side voice signal is a silence signal or not, and applies the voice recognition to a transmitter-side voice signal and a receiver-side voice signal which have been applied time-division process on the basis of the detection result.
However, when only one voice of a speaker is determined as a target of recognition, even when another speaker utters a keyword for determining whether a call is a call to be detected or not, it is difficult to detect the keyword. As a result, the precision of detecting a call of specific content may deteriorate. In addition, when a sound signal is a target of voice recognition, most of voice uttered by the speaker becomes a target of voice recognition. Consequently, reduction in process load may be insufficient.